Accurately determining certain physical properties of materials in a cost-effective, simple and reliable manner is an ongoing need in virtually all manufacturing industries. Precise knowledge of a material's properties enables a manufacturer to judiciously select and employ the appropriate material for an intended use or application. A specific example of an industrial practice wherein identifying suitable materials remains a somewhat crude and imprecise exercise is the selection of release papers for use with adhesive substances and products.
Release paper is used to store and protect tape, labels, stickers and other adhesives, because release paper can be removed prior to application of the adhesive to be the desired object or surface. Release paper permits the storage of pressure sensitive adhesive tape, labels and the like, while generally preserving the adhesive's tackiness. Release papers are typically coated with a thin layer of silicon or other low surface energy material in order to minimize the bond between the release paper and the adhesive.
The surface energy of release paper is very important in the tape, label and sticker industry. The surface energy of the release paper is directly proportional to the amount of adhesive substance that will remain on the release paper upon separation of the release paper and adhesive. Conversely, the degree of release of the paper is inversely proportional to its surface energy.
In the adhesives industry, it is often desirable to precisely determine how easy it is to peel off the release paper from the adhesive. The precise determination of tackiness is needed in order to determine potential uses in the industry. Currently, the degree of release is determined by commercially available mechanical testing instruments which measure the force required to peel a sample of release paper from an adhesive. Among the problems with these instruments are that they are expensive, cumbersome, imprecise and cannot be used in on-line quality control.
Sheet materials have long been tested for certain properties, such as printability and absorbency. The testing methods and apparatus for such materials have generally centered on the printing industry. Common methods and apparatus for testing the absorbency, printability or porosity of paper are taught, for example, in U.S. Pat. Nos. 4,259,862, 4,803,872, 4,911,003, 4,976,138 and 5,065,620. These patents do not disclose methods or means for testing the surface energy or releasability of the materials.
U.S. Pat. Nos. 4,541,273 and 5,141,767 describe measurement of tackiness and irregularities of surfaces, including paper, through mechanical processes employing solid and powdered marker substances. Methods and apparatus for testing absorbency and other properties of materials are taught in U.S. Pat. Nos. 2,353,852, 2,868,062, 3,559,475, 3,731,529 and 5,325,713. These involve complicated visual, photoelectrical, electrical, gravitational and ultrasonic testing methods and means.
Still other industries, particularly high technology manufacturing industries, have a need for precise and reliable on-line methods by which to determine certain properties of materials and tools used therein. The information provided by such methods would provide the interested manufacturer with information necessary to optimize tool service life, product quality and manufacturing efficiency.
An advantage exists, therefore, for a chemical testing system including method and apparatus for inexpensively, conveniently and precisely measuring properties of materials including, but not limited to, certain surface properties of substantially planar sheet materials and materials configured as regularly or irregularly surfaced three dimensional objects. Another advantage exists for such a method and apparatus that can be used in on-line quality control.
Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments of methods and apparatus of practicing the invention proceeds.